There are two methods for transmission between a device such as a memory card and a host such as a personal computer: a transmission method using a single-ended signal (hereinafter, referred to as “single-ended method”) and a transmission method using a differential signal (hereinafter, referred to as “differential method”).
The single-ended method has an advantage of having an interface circuit with a simple circuit structure, compared with the differential method. On the other hand, the differential method has an advantage of realizing fast transmission, compared with the single-ended method.
When an existing system employs the single-ended method as a transmission method between a device and a host, and a transmission speed therebetween is desired to be faster, a system supporting both the single-ended method and the differential method may be introduced, in view of compatibility with the existing system.
In such a system, each of the device and the host includes both of an interface circuit corresponding to the single-ended method and an interface circuit corresponding to the differential method.
As a technology that reduces the number of signal wires in a system supporting both of the single-ended method and the differential method, a technology described in Patent Literature 1 is known, for example.
According to this technology, a single-ended signal and a differential signal share signal wires so as to reduce the number of signal wires.
On the other hand, when a differential signal receiving circuit for receiving a differential signal is active to receive the differential signal, a specific amount of electric power is consumed even if a valid differential signal is not being received.
As a technology for reducing electric power consumption of the differential signal receiving circuit while a valid differential signal is not being received, a technology described in Patent Literature 2 is known, for example.
According to this technology, a host controls an active state or an inactive state of a device differential signal receiving circuit, using signal wires for transmitting a differential signal.
Here, when the host wants to activate the device differential signal receiving circuit that has been inactive, the host transmits, to the device, a single-ended signal for activating the differential signal receiving circuit. Then when the host wants to inactivate the device differential signal receiving circuit that has been active, the host transmits, to the device, a command (hereinafter, referred to as “stop command”) composed of a differential signal for inactivating the differential signal receiving circuit.
In order to control an active state or an inactive state of the differential signal receiving circuit connected to shared signal wires for transmitting both a single-ended signal and a differential signal using the technology described in Patent Literature 2, it can be realized by using signal wires for transmitting only a differential signal, which are different from the shared signal wires for transmitting both signals.